JP2009117364A - Membrane-electrode assembly for fuel cell and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane-electrode assembly for a fuel cell, and to provide its manufacturing method. <P>SOLUTION: The membrane-electrode assembly for a fuel cell and its manufacturing method are provided herein. The membrane-electrode assembly for a fuel cell includes: a proton exchange membrane; and electrodes respectively arranged on both surfaces of the proton exchange membrane. Each electrode includes a gas diffusion layer and a catalyst layer. The catalyst layer is arranged between the proton exchange membrane and the gas diffusion layer. The gas diffusion layer includes a carbon nanotube structure. The carbon nanotube structure includes carbon nanotubes tangled with each other. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a membrane-electrode assembly for a fuel cell and a manufacturing method thereof, and more particularly to a membrane-electrode assembly for a fuel cell using carbon nanotubes and a manufacturing method thereof.

  A fuel cell is a power generator that converts chemical energy stored in fuel and oxidant directly into electrical energy through an electrode reaction. Fuel cells have the advantages of high energy conversion rate, low environmental pollution, wide application range, no noise, and continuous operation, so they can be used in areas such as military, national defense, electric power, automobile and communication. Widely applied.

  A fuel cell has three types, an alkaline storage battery, a solid electrolyte fuel cell, and a solid polymer fuel cell (see Non-Patent Document 1). Recently, polymer electrolyte fuel cells have been remarkably developed and attracting increasing attention.

  The basic structure of a polymer electrolyte fuel cell is a membrane-electrode assembly (Membrane Electrode Assembly, MEA) in which a cathode, a solid polymer membrane (electrolyte), and an anode are integrated to form a reaction gas. A basic unit is formed by sandwiching a conductive plate called a bipolar plate engraved with a supply flow path, and this is particularly called a single cell. A single cell generates a voltage of about 0.7 V during operation. A structure in which the single cells are stacked and connected in series so as to obtain a high voltage is called a cell cell stack.

  Each of the cathode and anode includes a catalyst layer and a gas diffusion layer (abbreviated as GDL), and the catalyst layer is disposed between the gas diffusion layer and the solid polymer membrane. The The material of the solid polymer membrane includes perfluorosulfonic acid, polystyrene sulfonic acid, polystyrene trifluoroacetic acid, phenol-formaldehyde hydrogenated resin, and phenol-formaldehyde hydrogenated resin. hydrocarbons). The catalyst layer includes a catalyst material and a support. The catalyst material is, for example, metal particles such as platinum, gold, or ruthenium. The carrier is, for example, carbon particles such as graphite, carbon black, carbon fiber, or carbon nanotube. The gas diffusion layer is made of a treated carbon cloth or carbon paper.

  When using a fuel cell having the membrane-electrode assembly, the fuel gas and the electrodes installed on both surfaces of the solid polymer membrane of the membrane-electrode assembly are passed through the flow field plate using the relevant components. A gas to be oxidant is injected. The fuel gas is hydrogen gas, and the gas used as the oxidant is oxygen gas or air containing oxygen gas. The electrode for injecting the fuel gas is an anode, and the electrode for injecting the gas as the oxidant is a cathode. After the hydrogen gas enters the anode of the fuel cell at one end of the fuel cell, hydrogen molecules react as follows by the action of the catalyst.

H ₂ → 2H ⁺ + 2e ⁻

  Hydrogen ions generated from the reaction reach the cathode through the solid polymer membrane. At the same time, the electrons generated from the reaction reach the cathode by an external circuit (not shown).

  After the oxygen gas is injected into the cathode at the other end of the fuel cell, the oxygen gas reacts with the hydrogen ions and electrons as follows.

1 / 2O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O

In the course of the electrochemical reaction, when an external circuit is connected, the electrons form a current and can output electrical energy to the load through an appropriate connection. Water generated from the reaction is discharged through the gas diffusion layer and the flow field plate. The fuel gas and the gas used as the oxidant diffuse into the catalyst layer through the gas diffusion layer. Electrons necessary for the reaction and electrons generated from the reaction are transmitted by connecting the gas diffusion layer and an external circuit. Therefore, the material selection and manufacturing method of the gas diffusion layer has an important influence on the performance of the polymer electrolyte fuel cell.
Recent advances in fuel cell technology and its application, Journal of Power Sources, 2001, Vol. 100, p. 60-66 Kaili Jiang, Quung Li, Shuushan Fan, “Spinning continuous carbon nanotube yarns”, Nature, 2002, vol. 419, p. 801

  However, at present, carbon fiber paper is used as a gas diffusion layer used in a membrane-electrode assembly of a fuel cell. A conventional method for producing carbon fiber paper is to produce carbon fiber paper after mixing carbon fiber, wood pulp and cellulose fiber to produce paper pulp. Since the carbon fiber distribution in the carbon fiber paper is not uniform, the gas diffusion layer using the carbon fiber paper having the above structure has a drawback that the reaction gas cannot be diffused uniformly. Moreover, since the resistivity of the conventional carbon fiber paper is large, electrons for causing the gas diffusion layer to function and electrons generated from the gas diffusion layer cannot be conducted well. Due to the above-mentioned drawbacks, the electrochemical performance such as the reaction activity of the membrane-electrode assembly of the fuel cell is deteriorated. Further, conventional carbon fiber paper is inconvenient for processing because of poor toughness.

  Accordingly, the present invention provides a fuel cell membrane-electrode assembly that has better reaction activity and is convenient for processing, and a method for producing the same.

  In a membrane-electrode assembly including a solid polymer membrane and electrodes respectively installed on both surfaces of the solid polymer membrane, the electrode includes a gas diffusion layer and a catalyst layer, and the catalyst layer is the solid polymer The gas diffusion layer is disposed between a film and the gas diffusion layer, and the gas diffusion layer includes a carbon nanotube structure, and the carbon nanotube structure includes carbon nanotubes entangled with each other.

  In the carbon nanotube structure, the carbon nanotubes are isotropically and uniformly arranged irregularly.

  In the carbon nanotube structure, a single carbon nanotube has a length of 10 micrometers or more.

  In the carbon nanotube structure, the carbon nanotubes are entangled by intermolecular force to form a network structure.

  The carbon nanotube structure has a plurality of micropore structures, and a single micropore structure has a pore diameter of 100 micrometers or less.

  In the carbon nanotube structure, the thickness of the gas diffusion layer is 1 micrometer to 2 millimeters.

  A fuel cell membrane-electrode assembly manufacturing method includes a first step of manufacturing a carbon nanotube structure as a gas diffusion layer, and a second step of forming a catalyst layer on the surface of the gas diffusion layer to form an electrode. And a third step of providing a solid polymer membrane, installing the electrodes on both surfaces of the solid polymer membrane, and forming a membrane-electrode assembly of a fuel cell.

  The first step of producing a carbon nanotube structure as the gas diffusion layer is a first sub-step of providing a carbon nanotube raw material, and immersing the carbon nanotube raw material in a solvent to treat the carbon nanotube raw material. A second sub-step of forming a carbon nanotube structure having a fluff structure and a third sub-step of forming a carbon nanotube structure by filtering the carbon nanotube structure having the fluff structure.

  Compared with the membrane-electrode assembly of the conventional fuel cell, in the membrane-electrode assembly of the fuel cell of the present invention, the gas diffusion layer includes a carbon nanotube structure. Since the carbon nanotubes in the carbon nanotube structure are isotropically, uniformly and irregularly arranged, the carbon nanotube structure includes a large number of uniformly distributed microporous structures, and the carbon nanotube Has a large specific surface area. This structure can diffuse hydrogen gas and an oxidizing agent gas effectively and uniformly.

  Since the resistivity of the carbon nanotube is smaller than the resistivity of the carbon fiber, the resistivity of the carbon nanotube structure is smaller than the resistivity of the conventional carbon fiber paper, and the electrons necessary for the reaction and the electrons generated from the reaction are reduced. Can communicate effectively. Accordingly, the gas diffusion layer of the membrane-electrode assembly of the fuel cell enhances the reaction activity of the membrane-electrode assembly.

  In the carbon nanotube structure, a plurality of carbon nanotubes are attracted to each other by intermolecular force and entangled with each other to form a network structure. The carbon nanotube structure has good toughness, and has a different shape. Used for manufacturing membrane electrodes.

  Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1)
The present embodiment provides a membrane-electrode assembly 10 of a fuel cell. The fuel cell membrane-electrode assembly 10 includes a solid polymer membrane 12 and two electrodes 14. The electrode 14 includes a gas diffusion layer 16 and a catalyst layer 18. The electrodes 14 are respectively installed on both surfaces of the solid polymer film 12, and the catalyst layer 18 is installed between the solid polymer film 12 and the gas diffusion layer 16.

  The gas diffusion layer 16 includes a carbon nanotube structure. The carbon nanotube structure is a self-supporting structure composed of a plurality of carbon nanotubes. The plurality of carbon nanotubes are intertwined with each other. The carbon nanotube structure has a thickness of 1 micrometer to 2 millimeters. In the carbon nanotube structure, the carbon tubes are isotropically and irregularly arranged to form many microporous structures, and the diameter of the microporous structures is 100 micrometers or less. Since the resistivity of the carbon nanotube is smaller than the resistivity of the carbon fiber, the resistivity of the carbon nanotube structure is smaller than the resistivity of the conventional carbon fiber paper. In the carbon nanotube structure, a plurality of carbon nanotubes are entangled with each other by an intermolecular force (van der Waals force) to form a network structure, and the carbon nanotube structure has good toughness.

The catalyst layer 18 includes metal particles and carbon particles. The metal particles are platinum, gold or ruthenium, and platinum is preferable. The carbon particles are graphite, carbon black, carbon fiber, carbon nanotube, or the like, and carbon nanotubes are preferable. The metal particles are dispersed in the carbon particles, and the catalyst layer 18 is formed. The metal particles used as the catalyst material have a loading amount smaller than 0.5 mg / cm ² . The material of the solid polymer membrane 12 is perfluorosulfonic acid, polystyrene sulfonic acid, polystyrene trifluoroacetic acid, phenol-formaldehyde hydrogenated phenolic acid. (Hydrocarbons).

(Embodiment 2)
Referring to FIG. 2, the present embodiment provides a method for manufacturing a fuel cell membrane-electrode assembly 10. The manufacturing method includes the following steps.

  In the first step, a carbon nanotube structure is manufactured, and the carbon nanotube structure is used as the gas diffusion layer 16.

  The method for manufacturing the carbon nanotube structure includes the following sub-steps.

  In the first sub-step, a base material on which a carbon nanotube array is formed is provided, and the carbon nanotubes are peeled from the base material with a tool such as a knife to form a carbon nanotube raw material. The carbon nanotubes are intertwined with each other to some extent. In the carbon nanotube raw material, the length of the single carbon nanotube is 10 micrometers or more. The carbon nanotube array provided from this embodiment may include single-walled carbon nanotubes, double-walled carbon nanotubes, or multi-walled carbon nanotubes.

  In this embodiment, a chemical vapor deposition (CVD) method is adopted as a method for manufacturing the carbon nanotube array. The manufacturing method includes the following steps. In step (a), a flat substrate is provided, and the substrate is any one of a P-type silicon substrate, an N-type silicon substrate, and a silicon substrate on which an oxide layer is formed. In this embodiment, it is preferable to select a 4-inch silicon substrate. In step (b), a catalyst layer is uniformly formed on the surface of the substrate. The material of the catalyst layer is any one of iron, cobalt, nickel and alloys of both of them. In step (c), the substrate on which the catalyst layer has been formed is annealed with air at 700 ° C. to 900 ° C. for 30 minutes to 90 minutes. In step (d), the annealed substrate is placed in a reaction furnace, heated with a protective gas at a temperature of 500 ° C. to 740 ° C., and then a carbon-containing gas is introduced to react for 5 to 30 minutes. Thus, a super-aligned carbon nanotube array (Non-patent Document 2) can be grown. The carbon nanotube array has a height of 100 micrometers or more. The carbon nanotube array is composed of a plurality of carbon nanotubes that grow parallel to each other and perpendicular to the substrate. Since the carbon nanotube has a long length, the carbon nanotubes of the part are intertwined with each other. By controlling the growth conditions, the carbon nanotube array does not contain impurities such as amorphous carbon and remaining metal particles serving as the catalyst.

  In this embodiment, as the gas containing carbon, for example, active hydrocarbons such as acetylene, ethylene, and methane are selected, and it is preferable to select ethylene. The protective gas is nitrogen gas or inert gas, preferably argon gas.

  The carbon nanotube array provided from the present embodiment is not limited to being manufactured by the above manufacturing method, and may be manufactured by an arc discharge method or a laser evaporation method. The carbon nanotube array is used as a raw material.

  In the second sub-step, the carbon nanotube raw material is immersed in a solvent, and the carbon nanotube raw material is processed to form a fluffy carbon nanotube structure.

  After the carbon nanotube raw material is immersed in the solvent, the carbon nanotube is formed into a fluff structure by a method such as ultrasonic dispersion, high-strength stirring, or vibration. In this embodiment, the solvent is water or a volatile organic solvent. Treatment is performed for 10 to 30 minutes with respect to the solvent containing carbon nanotubes by an ultrasonic dispersion method. Since carbon nanotubes have a large specific surface area and a large intermolecular force between the carbon nanotubes, the carbon nanotubes are entangled and formed into a fluff structure.

  In the third sub-step, the carbon nanotube structure having the fluff structure is filtered to form a carbon nanotube structure. The carbon nanotube structure is used as the gas diffusion layer 16 of the membrane-electrode assembly 10 of the fuel cell.

  In this embodiment, first, a funnel on which filter paper is placed is provided. When the solvent containing the carbon nanotube structure having the fluff structure is applied to the funnel on which the filter paper is placed and left for a while and dried, the carbon nanotube structure having the fluff structure is separated. FIG. 3 shows a carbon nanotube structure having a fluff structure placed on the filter paper. From FIG. 3, it can be seen that the carbon nanotubes are entangled with each other to form an irregular fluff structure.

  The separated carbon nanotube structure of the fluff structure is placed in a container, the carbon nanotube structure of the fluff structure is expanded into a predetermined shape, a predetermined pressure is applied to the carbon nanotube structure of the fluff structure, and the fluff structure When the solvent remaining in the carbon nanotube structure is roasted or the solvent volatilizes naturally, a carbon nanotube structure is formed.

  In this embodiment, the thickness and surface density of the carbon nanotube structure can be controlled by the area where the carbon nanotube structure having the fluff structure is developed. That is, the fluff structure carbon nanotube structure having a certain volume has a smaller thickness and areal density as the developed area increases. The carbon nanotube structure has a thickness of 1 micrometer to 2 millimeters and a width of 1 centimeter to 10 centimeters. FIG. 4 shows a carbon nanotube structure formed in this embodiment.

  A carbon nanotube structure is formed using a microporous membrane and an air-pumping funnel. Specifically, a microporous membrane and an air pump funnel are provided, and the solvent containing the fluffy carbon nanotube structure is passed through the microporous membrane to the air pump funnel, and then extracted to the air pump funnel and dried. A carbon nanotube structure is formed. The microporous film has a smooth surface. In the microporous membrane, the diameter of a single micropore is 0.22 μm. Since the microporous membrane has a smooth surface, the carbon nanotube structure can be easily peeled off from the microporous membrane. Furthermore, since the air pump is used to apply air pressure to the fluffy carbon nanotube structure, a uniform carbon nanotube structure can be formed.

  In the carbon nanotube structure manufactured from the present embodiment, the entangled carbon nanotubes are attracted to each other by intermolecular force to form a network structure, so that the carbon nanotube structure has good toughness. Since the carbon nanotube structure has flexibility, the carbon nanotube structure can be folded into an arbitrary shape, which is convenient for processing. FIG. 5 is a photograph of the carbon nanotube structure manufactured from the present embodiment folded.

  In the present embodiment, the carbon nanotube structure can be cut in any shape and size according to actual application, and can be applied to the gas diffusion layer 16 of a small fuel cell, which is beneficial for expanding the application range. is there.

  In the second step, the catalyst layer 18 is manufactured on one surface of the gas diffusion layer 16 to form the electrode 14.

  The method for manufacturing the catalyst layer 18 includes the following steps.

  First, a mixture of metal particles and carbon particles is placed in a solution, and water and a surfactant are added to the solution to disperse the mixture, thereby forming a catalyst pulp.

The metal particles as the catalyst material are any one of platinum, gold, and ruthenium. The carbon particles as the carrier are any one of graphite, carbon black, carbon fiber, and carbon nanotube. The metal particles are supported on the surface of the carbon particles as the carrier, and dispersed particles are formed. The amount of the metal particles supported is set to be 0.5 mg / cm ² or less. The carbon particles have high conductivity, high specific surface area, and corrosion resistance. The solution is formed by dissolving CHF1000 resin in dimethylacetamide. The concentration of the resin contained in the solution is 5 wt%. The surfactant suppresses the aggregation of carbon particles, and for example, isopropyl alcohol can be used. In order to uniformly disperse the carbon particles in the catalyst agent pulp, before producing the catalyst agent pulp, the carbon particles can be polished by a ball mill to reduce the diameter of the carbon particles. As a method for dispersing the carbon particles, a method of stirring with ultrasonic waves or high intensity can be used.

  Next, the catalyst pulp is applied to one surface of the gas diffusion layer 16 and dried to form the catalyst layer 18.

  The method for applying the catalyst pulp is one of a sputtering method, a dipping method, and a screen printing method. As a method for drying the catalyst agent pulp, it is possible to dry under a low temperature condition or to use a baking method. Thereby, it is possible to prevent the catalyst layer 18 from penetrating into the soot or the gap.

  In the third step, the solid polymer membrane 12 is provided, and the electrodes 14 are installed on both surfaces of the solid polymer membrane 12 to form the fuel cell membrane-electrode assembly 10.

  The electrodes 14 can be bonded to both surfaces of the solid polymer film 12 by hot pressing. The catalyst layer 18 of the electrode 14 is adjacent to the surface of the solid polymer membrane 12 and is disposed between the gas exchange layer 16 and the solid polymer membrane 12. The material of the solid polymer film 12 is any one of perfluorosulfonic acid, polystyrene sulfonic acid, polystyrene trifluoroacetic acid, phenol resin acid, and hydrocarbon.

  In the present embodiment, the method for manufacturing the gas diffusion layer 16 has the following advantages. By processing the carbon nanotube raw material, the carbon nanotubes are entangled with each other, and the manufactured carbon nanotube structure has good toughness. The manufacturing method can control the thickness and surface density of the carbon nanotube structure in the manufacturing process, has a simple process, and is convenient for actual application.

(Embodiment 3)
Referring to FIG. 6, the present invention provides a fuel cell 600. The fuel cell 600 includes a membrane-electrode assembly 618, two flow field plates 610, two current collectors 612 and associated components 614.

  The membrane-electrode assembly 618 includes a solid polymer membrane 602 and two electrodes 604. The single electrode 604 includes a gas diffusion layer 606 and a catalyst layer 608. The electrodes 604 are installed on both surfaces of the solid polymer film 602, and the catalyst layer 608 is installed between the solid polymer film 602 and the gas diffusion layer 606. The gas diffusion layer 606 is a carbon nanotube structure. The catalyst layer 608 includes metal particles and carbon particles. The metal particles are platinum, gold or ruthenium, and platinum is preferred. The carbon particles are graphite, carbon black, carbon fiber, carbon nanotube, or the like, with carbon nanotubes being preferred. The material of the solid polymer film 602 is perfluorosulfonic acid, polystyrene sulfonic acid, polystyrene trifluoroacetic acid, phenol resin acid or hydrocarbon. The solid polymer membrane 602 is used to conduct protons and separate a fuel gas and an oxidant gas.

  The flow field plate 610 is installed on the surface of the gas diffusion layer 606 of the electrode 604 and is used to conduct fuel gas, gas as an oxidant, and water as a reactant. The flow field plate 610 is made of a metal or a conductive carbon material. One or a plurality of flow field tanks 616 are installed on one surface of the flow field plate 610. The flow field tank 616 is installed adjacent to the gas diffusion layer 606 and is used to guide and conduct the fuel gas, the gas as the oxidizer, and the water as the reactant. The current collector 612 is made of a conductive material, and is installed on the surface of the flow field plate 610 facing the surface on which the electrode 604 is installed. The current collector 612 is used to collect and transmit electrons generated when the fuel cell 600 is operated.

  The related parts 614 include a blower, a tube, a valve, and the like. The blower is connected to the flow field plate 610 by a tube, and is used for providing the fuel cell 600 with fuel gas and oxidant gas.

  When the fuel cell 600 is used, fuel gas and oxidant gas are passed from the flow field plate 610 through the related component 614 and installed on both surfaces of the solid polymer membrane 602 of the membrane-electrode assembly 618. Injection into the electrode 604 is performed. The fuel gas is hydrogen gas, and the oxidant gas is oxygen gas or air containing oxygen gas. The hydrogen gas is injected into the anode (not shown) through the flow field tank 616, and the oxidant gas is injected into the cathode (not shown) through the flow field tank 616.

  After the hydrogen gas is injected into the anode at one end of the fuel cell 600, the following reaction occurs.

H ₂ → 2H ⁺ + 2e ⁻

  Hydrogen ions generated from the reaction reach the cathode through the solid polymer membrane 602. At the same time, the electrons generated from the reaction reach the cathode in an external circuit (not shown).

  After the oxygen gas is injected into the cathode at the other end of the fuel cell 600, the oxygen gas reacts with the hydrogen ions and electrons as follows.

1 / 2O ₂ + 2H ⁺ + 2e → H ₂ O

  In the electrochemical reaction, the electrons form a current and electrical energy is released.

  Water generated in the reaction process can be discharged to the outside of the membrane-electrode assembly 618 through the gas diffusion layer 606 and the flow field plate 610. In the reaction process, the flow field plate 610 is used as a channel and can transmit fuel gas, oxidizing gas, and electrons. Using the flow field plate 610, the fuel gas and the oxidizing gas can be transmitted to the catalyst layer, and electrons can be transmitted to an external circuit connected to the flow field plate 610.

  In the present embodiment, the gas diffusion layer 606 includes a carbon nanotube structure. The carbon nanotubes in the carbon nanotube structure are wound around each other and are isotropically and uniformly arranged irregularly. The carbon nanotube structure has a plurality of micropore structures that are uniformly distributed. The carbon nanotube structure has a very large specific surface area.

  Accordingly, hydrogen gas can diffuse effectively and uniformly into the carbon nanotube structure at one end of the fuel cell 600. Since the hydrogen gas uniformly contacts the metal particles of the catalyst layer 608, the reaction that occurs between the metal particles and the hydrogen gas is highly activated. At the other end of the fuel cell 600, the oxygen gas is uniformly diffused into the catalyst layer 608 by the carbon nanotube structure, so that the oxygen gas can sufficiently contact the metal of the catalyst layer 608. Therefore, the reaction that occurs between the metal particles and the hydrogen ions and electrons is highly activated. Since the carbon nanotube structure has good conductivity, the electrons can be transferred to the carbon nanotube structure faster.

It is a figure which shows the structure of the membrane-electrode assembly of the fuel cell which concerns on embodiment of this invention. 3 is a flowchart of a method for manufacturing a membrane-electrode assembly of a fuel cell according to an embodiment of the present invention. 2 is a photograph of a carbon nanotube structure having a fluff structure manufactured from an embodiment of the present invention. 3 is a photograph of a carbon nanotube structure having a predetermined shape manufactured from an embodiment of the present invention. 2 is a photograph of a carbon nanotube structure produced from an embodiment of the present invention folded. It is a figure which shows the structure of the fuel cell which concerns on embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Membrane-electrode assembly 12 Solid polymer membrane 14 Electrode 16 Gas diffusion layer 18 Catalyst layer 600 Fuel cell 602 Solid polymer membrane 604 Electrode 606 Gas diffusion layer 608 Catalyst layer 610 Flow field plate 612 Current collector 614 Related parts 616 Flow Field tank

Claims (8)

In a membrane-electrode assembly comprising a solid polymer membrane and electrodes respectively installed on both surfaces of the solid polymer membrane,
The electrode includes a gas diffusion layer and a catalyst layer;
The catalyst layer is disposed between the solid polymer membrane and the gas diffusion layer;
The gas diffusion layer includes a carbon nanotube structure;
A membrane-electrode assembly of a fuel cell, wherein the carbon nanotube structure includes carbon nanotubes intertwined with each other.   2. The fuel cell membrane-electrode assembly according to claim 1, wherein in the carbon nanotube structure, the carbon nanotubes are isotropically and uniformly arranged irregularly.   3. The fuel cell membrane-electrode assembly according to claim 1, wherein in the carbon nanotube structure, a single carbon nanotube has a length of 10 μm or more. 4.   The membrane-electrode of a fuel cell according to any one of claims 1 to 3, wherein in the carbon nanotube structure, the carbon nanotubes are entangled by intermolecular force to form a network structure. Joined body. The carbon nanotube structure has a plurality of microporous structures;
The membrane-electrode assembly of a fuel cell according to any one of claims 1 to 4, wherein the pore diameter of the single microporous structure is 100 micrometers or less.   6. The fuel cell membrane-electrode assembly according to claim 1, wherein in the carbon nanotube structure, the gas diffusion layer has a thickness of 1 micrometer to 2 millimeters. . A first step of producing a carbon nanotube structure as a gas diffusion layer;
A second step of forming a catalyst layer on the surface of the gas diffusion layer to form an electrode;
Providing a solid polymer membrane, placing the electrodes on both surfaces of the solid polymer membrane, respectively, and forming a fuel cell membrane-electrode assembly;
A method for producing a membrane-electrode assembly for a fuel cell, comprising: The first step of producing a carbon nanotube structure as the gas diffusion layer is:
A first sub-step of providing carbon nanotube raw materials;
A second sub-step of immersing the carbon nanotube raw material in a solvent and treating the carbon nanotube raw material to form a fluffy carbon nanotube structure;
A third sub-step of forming a carbon nanotube structure by filtering the carbon nanotube structure of the fluff structure;
The method for producing a membrane-electrode assembly for a fuel cell according to claim 7, comprising: